Support runtime access in Vite for prefixed vars (e.g. `VITE_*`)

[yamcodes]

When using @arkenv/vite-plugin in a Vite + React project, the plugin validates environment variables at build time but doesn't provide a type-safe way to access them in the frontend runtime. Vite only exposes environment variables prefixed with VITE_ to import.meta.env, but there's no exported, validated env object to import.

Steps to Reproduce:

1. Create a React template with Vite.
2. Install @arkenv/vite-plugin and configure it in vite.config.ts.
3. Try to import the validated env object in frontend code.
4. Result: No env object is exported, must manually access import.meta.env.VITE_*.

Expected behavior:

The plugin should export a type-safe env object that can be imported in frontend code, similar to how createEnv works in Node environments.

Current workaround:

Manually access each variable via import.meta.env:

// No type safety, no validation at runtime
const apiUrl = import.meta.env.VITE_API_URL;

Desired API:

import { env } from "virtual:arkenv";

// Type-safe and validated
const apiUrl = env.VITE_API_URL;

Related:

• Support Bun frontend process.env prefixing (e.g. BUN_PUBLIC_*) #181 (Bun frontend process.env prefixing)
• bug: vite typescript does not infer the environment variables type. #195 (Alternative approach to support typesafe access in Vite, via import.meta.env)

Action Items:

• Export a virtual module that provides the validated env object.
• Support configurable prefix (default: VITE_*).
• Ensure TypeScript types are generated for the virtual module.

[yamcodes]

Closing as not planned for now due to #366 being merged in